Hyaline cell-rich chondroid syringoma of the finger.

A mixed tumor is a neoplasm that has microscopic features of both epithelial and mesenchymal differentiation. Such mixed tumors are known as pleomorphic adenomas in the salivary glands, and their cutaneous counterparts are called chondroid syringomas. These tumors commonly occur in the head and neck region of middle-aged men. Hyaline cell-rich chondroid syringoma is a rare benign variant of chondroid syringoma composed of cells with eosinophilic hyaline cytoplasm and plasmacytoid features, the origin of which remains elusive. Although very few cases have been reported in literature, it is important to be aware of this entity so as to avoid misdiagnosis on histopathological examination. In this report we present a case of hyaline cell-rich chondroid syringoma occurring in the finger.

Introduction

Skin tumors present in a variety of clinical forms as a result of which they enter into the differential diagnoses of a number of conditions presenting as swellings in the skin and subcutaneous tissue. The cutaneous adnexal neoplasms, in themselves, constitute a wide spectrum because they can differentiate along one or more of the adnexal lineages. Among the adnexal tumors, the mixed tumor of the skin, also known by the name chondroid syringoma, is an important adnexal neoplasm that shows evidence of both epithelial and mesenchymal differentiation.[1] Although around 400 cases of chondroid syringomas have been reported worldwide, only eight cases of hyaline cell–rich chondroid syringoma have been reported till 2002.[23] We report here a case of hyaline cell-rich chondroid syringoma which was also unusual in its location.

Case Report

A 45-year-old female presented with a slow-growing, painless swelling in the tip of her left index finger since 1 year. This swelling was a single, firm, well-circumscribed mass measuring around 2.5 cm in diameter. A clinical diagnosis of implantation dermoid was made and an excision biopsy was performed and the specimen sent for histopathological evaluation.

Grossly, the tumor was a globular, well-circumscribed, firm, gray-white mass of 2.5 cm diameter, with a cut surface that was glistening white and punctuated by tiny cystic spaces.

Histopathological examination revealed a well-circumscribed proliferation of epithelial cells interspersed with foci of fibrous, myxoid, and chondroid stroma [Figures 1a and 1b]. Most of these cells, which were arranged in broad sheets and nests, had a plasmacytoid appearance with an ovoid eccentric nucleus having fine granular chromatin and a deeply eosinophilic ′hyaline-like′ cytoplasm [Figure 2]. Interconnecting tubuloalveolar structures lined by two layers of cuboidal epithelial cells and ductal structures lined by one- to two-layered epithelial cells were also evident [Figure 3]. Focal keratinous differentiation in the form of a keratinous cyst was also noted. The stroma showed intense positivity with periodic acid-Schiff (PAS) and alcian blue stain and metachromatic staining with toluidine blue. This constellation of findings led to the diagnosis of hyaline cell–rich chondroid syringoma.

Figure 1

(a)Well-circumscribed proliferation of epithelial cells interspersed with foci of fibrous and myxoid stroma (H and E; 100×) b: Proliferation of epithelial cells interspersed with foci of fibrous and myxoid stroma (H and E; 400×)

Figure 2

Broad sheets of plasmacytoid ‘hyaline cells’ (H and E; 400×)

Figure 3

Tubuloalveolar structures lined by bi layered epithelium (H and E; 400×)

Discussion

Chondroid syringoma or cutaneous mixed tumor is a rare adnexal neoplasm with a very low incidence of 0.01%–0.098%.[4] Morphologically it is considered to be the cutaneous counterpart of the pleomorphic adenoma of salivary glands, but differs from it in that it rarely recurs.[2] Typically, the tumor is seen in the head and neck region as a slow-growing, painless, subcutaneous nodule.[25] In the present case, the lesion was found at the tip of the index finger – an unusual location. There have been occasional reports of these tumors occurring at such uncommon sites.[67] This lesion always occurs as a solitary nodule though, rarely, multiple tumors have been documented.[6] Middle-aged men are more commonly affected by this tumor. Clinically, this tumor can be mistaken for sebaceous cyst, dermoid, neurofibroma, calcifying epithelioma, solitary trichoepithelioma, etc.

Microscopy of a classical chondroid syringoma shows a well-circumscribed tumor that is located in the dermis and subcutaneous tissue with no connection to the overlying epidermis. There is epithelial cell proliferation admixed with a stroma that is fibrous, myxoid, and chondroid. The epithelial cells are arranged in nests, islands, or ductal and tubular structures. Some cases show follicular and sebaceous differentiation.

Hirsch and Helwig[1] proposed a set of criteria to be fulfilled for the diagnosis of chondroid syringoma; these are: 1) nests of cuboidal or polygonal cells; 2) intercommunicating tubuloalveolar structures lined by two or more rows of cuboidal cells; 3) ductal structures composed of one or two rows of cuboidal cells; 4) occasional keratinous cysts; and 5) a matrix of varying composition. A classical chondroid syringoma can satisfy most of these criteria although in some only the epithelial and stromal components predominate. In the present case all the criteria were fulfilled.

Chondroid syringomas can be either derived from the eccrine or the apocrine glands. Headington classified the chondroid syringomas into two types based on the morphology. The apocrine type or type I chondroid syringoma is the most common type and in this form a tubulocystic pattern of the epithelium is noted. The lining is usually two cells thick, with focal decapitation secretion. The eccrine type or the type II chondroid syringoma shows uniform small round tubules lined by a single layer of cuboidal epithelial cells. The present case was of the apocrine type according to Headington's criteria.[25] Rarely, these tumors may be large.[8] A malignant variant of chondroid syringoma has also been described.[9]

In some cases the epithelial cells are predominantly plasmacytoid in nature and such lesions are termed as hyaline cell–rich chondroid syringoma or hyaline cell–rich apocrine mixed tumor. These hyaline cells represent aberrant myoepithelial differentiation. It is important to recognize this entity as it can be morphologically confused for a malignant melanoma or an extra-skeletal chondrosarcoma.[310] In the present case although the plasmacytoid cells predominated, the additional findings of a tubulocystic pattern of the epithelium, along with the varied composition of the stroma, helped in arriving at the diagnosis of hyaline cell–rich chondroid syringoma. This diagnostic entity is very rare, with only nine cases having been reported all over the world to the best of our knowledge.[3]

Although recurrences are uncommon, malignancy arising in a setting of chondroid syringoma is well known. Hence, histopathological examination is advisable in all such cases. Although the lesion is rare, it has to be kept in mind when formulating the differential diagnoses of such nodules. The histopathologist must also be aware of this entity, including the hyaline cell-rich variant, to avoid potential misdiagnosis.